Patent GB-766803-A (GB)
Title: Improvements in or relating to the manufacture of porous sheet or strip material
IPC: H01G9/04
Filed: 1953-10-27
Abstract: A method of making porous sheet or strip material comprises feding particulate material through a heating zone and spraying the particles on a relatively moving base, the arrangement being such that the exterior only of the particles is rendered molten or plastic by passage through the heating zone while they remain interiorly solid and the exteriors of adjacent particles fuse together to form a coherent porous mass (see Group V). The heat zone is conveniently a flame, and the temperature of the flame and the time the particles are in it are controlled so that only the outside surfaces of the particles are melted.  The particles are projected from, e.g. a spray gun at a constant rate so that they will unite into a continuous porous sheet, and to ensure that this rate will be constant they may be supplied to the gun by a hopper and belt or screw feed, the rate of supply being co-ordinated with the speed of the moving base. Instead of a spray gun, a vibrating screen dropping the particles may be used.  With spray deposition, to ensure uniform density, multiple spraying may be used arranged for the thinner parts of the sprays to overlap.  A satisfactory particle size is from 2 to 8 microns.  The particles may be deposited on a temperature-controlled continuously-moving polished metal base, e.g. the surface of a fluid-cooled drum, or a fine mesh metallic screen, e.g. stainless steel mesh, with chilling effected by coolant propelled by fans or pumps.  The particles are immediately chilled and solidified on meeting the base and the layer or sheet formed by their uniting is stripped by a doctor knife and drawn on to a roll.  The deposition may be directly on the base or on a fibrous web, e.g. paper or gauze, located on the base, the deposited layer and the web being removed as a composite material.  In an illustrated example polystyrene particles of 60 to 150 mesh are sprayed in a gas stream through a flame at a temperature of 500 DEG  to 1300 DEG  F. on to a metal drum which is cooled by fluid introduced through its hollow shaft and whose surface is kept polished by a felt lubricator and polisher.ALSO:A method of making porous sheet or strip material comprises feeding particulate material through a heating zone and spraying the particles on a relatively moving base, the arrangement being such that the exterior only of the particles is rendered molten or plastic by passage through the heating zone while they remain interiorly solid and the exterior of adjacent particles fuse together to form a coherent porous mass (see Group V).  The heat zone is conveniently a flame, and the temperature of the flame and the time the particles are in it are controlled so that only the outside surfaces of the particles are melted.  The particles are projected from, e.g., a spray gun at a constant rate so that they will unite into a continuous porous sheet, and to ensure that this rate will be constant they may be supplied to the gun by a hopper and belt or screw feed, the rate of supply being co-ordinated with the speed of the moving base.  Instead of a spray gun, a vibrating screen dropping the particles may be used. With spray deposition, to ensure uniform density, multiple spraying may be used arranged for the thinner parts of the sprays to overlap.  A satisfactory particle size is from 2 to 8 microns. The particles may be deposited on a temperature - controlled continuously - moving polished metal base, e.g. the surface of a fluid-cooled drum, or a fine mesh metallic screen, e.g. stainless steel mesh, with chilling effected by coolant propelled by fans or pumps.  The particles are immediately chilled and solidified on meeting the base and the layer or sheet formed by their uniting is stripped by a doctor knife and drawn on to a roll.  The deposition may be directly on the base or on a fibrous web, e.g. paper or gauze, located on the base, the deposited layer and the web being removed as a composite material.  If metal, e.g. aluminium, particles are sprayed through a hot zone to melt their surfaces and on to a cold moving base, porous metal products result which are suitable for electrolytic condenser electrodes.  Metallic filter membranes and osmotic membranes may also be made according to the invention.ALSO:A method of making porous sheet or strip material comprises feeding particulate material through a heating zone and spraying the particles on a relatively moving base, the arrangement being such that the exterior only of the particles is rendered molten or plastic by passage through the heating zone while they remain interiorly solid and the exteriors of adjacent particles fuse together to form a coherent porous mass.  The heat zone is conveniently a flame, and the temperature of the flame and the time the particles are in it are controlled so that only the outside surfaces of the particles are melted.  The particles are projected from, e.g., a spray gun at a constant rate so that they will unite into a continuous porous sheet, and to ensure that this rate will be constant they may be supplied to the gun by a hopper and belt or screw feed, the rate of supply being co-ordinated with the speed of the moving base.  Instead of a spray gun, a vibrating screen dropping the particles may be used.  With spray deposition, to ensure uniform density, multiple spraying may be used arranged for the thinner parts of the sprays to overlap.  A satisfactory particle size is from 2 to 8 microns.  The particles may be deposited on a temperature-controlled continuously-moving polished metal base, e.g. the surface of a fluid-cooled drum, or a fine mesh metallic screen, e.g. stainless steel mesh, with chilling effected by coolant propelled by fans or pumps.  The particles are immediately chilled and solidified on meeting the base and the layer or sheet formed by their uniting is stripped by a doctor knife and drawn onto a roll.  The deposition may be directly on the base or on a fibrous web, e.g. paper or gauze, located on the base, the deposited layer and the web being removed as a composite material.  In an illustrated example polystyrene particles of 60 to 150 mesh are sprayed in a gas stream through a flame at a temperature of 500 DEG F. to 1300 DEG F. onto a metal drum which is cooled by fluid introduced through its hollow shaft and whose surface is kept polished by a felt lubricator and polisher.  Dielectric porous strips made according to the invention are suitable for use in electrolytic cells as separators, or as retainers for the active material on a battery storage plate in which case they may be sprayed on both faces of the plate, with or without a fibrous layer interposed, to conform to the shape of the plate and two of them, when placed round the plate, form a porous envelope.  The material of the particles must be one which does not react with an electrolyte, e.g. polystyrene.  The plastic separators may be extended upwards to support the terminals of an electrolytic cell. If, instead of plastic material, metal, e.g. aluminium, particles are sprayed through a hot zone to melt their surfaces and onto a cold moving base, porous metal products result which are suitable for electrolytic condenser electrodes.  Metallic filter membranes and osmotic membranes may also be made according to the invention.